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North

America:Juan

de Fuca

Pacific:Juan deFuca

North American:Pacific

40°N

35°N

30°N

40°N

35°N

30°N

110°W115°W120°W125°W

U.S. Department of the InteriorU.S. Geological Survey

Earthquake Summary Mapprepared in cooperation withthe Global Seismographic Network

Tectonic SummaryThe July 6th, 2019, 03:19 UTC (July 5th 20:19 locally) Mw 7.1 earthquake in easternCalifornia, southwest of Searles Valley, occurred as the result of shallow strike slipfaulting in the crust of the North America plate. Focal mechanism solutions for theearthquake indicate rupture occurred on a steeply dipping fault as the result of eitherright lateral slip on a plane striking NW-SE, or as left lateral slip on a plane strikingSW-NE. At the location of this earthquake, approximately 150 km northeast of SanAndreas Fault - the major plate boundary in the region – the Pacific plate moves tothe northwest with respect to the North America plate at a rate of approximately 48mm/yr. The location of the earthquake falls within the Eastern California shear zone, aregion of distributed faulting associated with motion across the Pacific:North Americaplate boundary, and an area of high seismic hazard. More detailed studies will berequired to precisely identify the causative fault associated with this event, thoughseismic activity over the past 2 days has been occurring on two conjugate faultstructures in the Airport Lake Fault Zone.

This earthquake occurs approximately 34 hours after and 11 km northwest of a M 6.4event in the same region, on July 4th, 2019, at 17:33 UTC. The July 4th event waspreceded by a short series of small foreshocks (including a M4.0 earthquake 30minutes prior), and was followed by a robust sequence of aftershocks, includingalmost 250 M 2.5+ earthquakes (up until the M 7.1 event). Those events aligned withboth nodal planes (NE-SW and NW-SE) of the focal mechanism solution of the M 6.4event, which was very similar in faulting style to today’s M 7.1 earthquake. Thesequence includes two other M5+ earthquakes, one of which occurred 20 secondsbefore the M 7.1 event. The M 7.1 earthquake occurred at the NW extension of theprior sequence.

While commonly plotted as points on maps, earthquakes of this size are moreappropriately described as slip over a larger fault area. Strike-slip-faulting events ofthe size of the July 6, 2019, earthquake are typically about 70x15 km (length xwidth).

This region of eastern California has hosted numerous moderate sized earthquakes.Over the past 40 years, prior to the July 4th event, 8 other M5+ earthquakes haveoccurred within 50 km of the July 6th, 2019 earthquake. The largest of these was a M5.8 event on September 20, 1995, just 3 km to the west of today’s event, which wasfelt strongly in the China Lake-Ridgecrest area, and more broadly from Los Angeles toLas Vegas.

0 175 350 525 70087.5Kilometers

Landslide Probability≤ .2%

.2 - 1%

1 - 2%

2 - 5%

5 - 10%

10 - 20%

> 50%

Liquefaction Probability≤ .05%

.2 - 1%

1 - 2%

2 - 5%

5 - 10%

10 - 20%

> 50%

18km W of Searles Valley, CA

06 July 2019 03:19:53 UTC

35.7695° Latitude, -117.5993333° LongitudeDepth: 8 kmMagnitude: 7.1

MainShock

Others

Divergent

Transform

Subduction#

Plate Boundaries

≥ 300!(

70 - 299!(

0 - 69!(

Earthquake Depth (km)

7.5 +!(M6.5 - M7.5!(

M5.5 - 6.5

Earthquake Magnitude

REFERENCES

Bird, P., 2003, An updated digital model of plate boundaries: Geochem. Geophys.Geosyst., v. 4, no. 3, pp. 1027-80.

Engdahl, E.R., and Villasenor, A., 2002, Global Seismicity: 1900-1999, chap. 41of Lee, W.H.K., and others, eds., International Earthquake and EngineeringSeismology, Part A: New York, N.Y., Elsevier Academic Press, 932 p.

Engdahl, E.R., Van der Hilst, R.D., and Buland, R.P., 1998, Global teleseismicearthquake relocation with improved travel times and procedures for depthdetermination; Bull. Seism. Soc. Amer., v. 88, p. 722 743.

DISCLAIMERBase map data, such as place names and political boundaries, are the bestavailable but may not be current or may contain inaccuracies and thereforeshould not be regarded as having official significance.

Map updated by U.S. Geological SurveyNational Earthquake Information Center09 July 2019https://earthquake.usgs.gov/Map not approved for release by Director USGS

Ground-Failure Models

DYFI/Shakemap

Seismic Hazard

DATA SOURCES

EARTHQUAKES AND SEISMIC HAZARD USGS, National Earthquake Information Center NOAA, National Geophysical Data Center IASPEI, Centennial Catalog (1900 - 1999) and extensions (Engdahl and Villaseñor, 2002)

EHB catalog (Engdahl et al., 1998)HDF (unpublished earthquake catalog, Engdahl, 2003)Global Seismic Hazard Assessment ProgramVolcanoes of the World (Siebert and Simkin, 2002)

PLATE TECTONICS AND FAULT MODELPB2002 (Bird, 2003)Ji, C., D.J. Wald, and D.V. Helmberger, Source descriptionof the 1999 Hector Mine, California earthquake; Part I:Waveletdomain inversion theory and resolution analysis, Bull. Seism.Soc. Am., Vol 92, No. 4. pp. 1192-1207, 2002.DeMets, C., Gordon, R.G., Argus, D.F., 2010.Geologically current plate motions, Geophys. J. Int. 181,1-80.

BASE MAPNIMA and ESRI, Digital Chart of the WorldUSGS, EROS Data CenterNOAA GEBCO and GLOBE Elevation Models

Seismic Hazard (m/s²)

.2

.4

.8

1.6

2.4

3.2

4.0

4.8

9.8

Estimated Economic Losses

Estimated Fatalities

Earthquake Impact

Yellow alert for economic losses. Some damage is possible and the impact should berelatively localized. Estimated economic losses are less than 1% of GDP of the UnitedStates. Past events with this alert level have required a local or regional levelresponse.

Recent earthquakes in this area have caused secondary hazards such as tsunamis,landslides and liquefaction that might have contributed to losses.

Overall, the population in this region resides in structures that are highly resistant toearthquake shaking, though some vulnerable structures exist. The predominantvulnerable building types are unreinforced brick masonry and reinforced masonryconstruction.

Ground-Failure